Mucopolysaccharidoses are a type of lysosomal storage disorder in which complex sugar molecules are not broken down normally and accumulate in harmful amounts in body tissues. The result is a characteristic facial appearance and abnormalities of the bones, eyes, liver, and spleen, sometimes accompanied by intellectual disability. Mucopolysaccharidoses occur when parents pass on to their children the defective genes that cause these disorders.
Mucopolysaccharidoses occur when the body lacks enzymes needed to break down and store complex sugar molecules.
Typically, symptoms include short stature, hairiness, stiff finger joints, and coarseness of the face.
The diagnosis is based on symptoms, a physical examination, and blood tests.
Treatment depends on the type and may include lifelong enzyme replacement therapy, and sometimes a bone marrow transplant.
Although a normal life span is possible, some types cause premature death.
There are different types of inherited disorders. In many hereditary metabolic disorders, both parents of the affected child carry 1 copy of the abnormal gene. Because usually 2 copies of the abnormal (recessive) gene are necessary for the disorder to occur, usually neither parent has the disorder. Some hereditary metabolic disorders are X-linked, which means only 1 copy of the abnormal gene can cause the disorder in boys. (See also Overview of Hereditary Metabolic Disorders.)
Complex sugar molecules called mucopolysaccharides (glycosaminoglycans) are essential parts of many body tissues. In mucopolysaccharidoses, the body lacks enzymes needed to break down (metabolize) and store mucopolysaccharides. As a result, excess mucopolysaccharides enter the blood and are deposited in abnormal locations throughout the body.
There are many types of mucopolysaccharidosis depending on which specific enzyme is missing. The types are classified by Roman numerals and sometimes also given a specific name (for example, Hurler syndrome and Hunter syndrome).
Symptoms of Mucopolysaccharidoses
Different types of mucopolysaccharidosis have slightly different symptoms but, in general, during infancy and childhood, short stature, coarse hair, and abnormal development become noticeable. The face may appear heavy with a large head, prominent forehead, short nose, and large lips and tongue. The arteries or heart valves can be affected. Finger joints are often stiff.
Some types of mucopolysaccharidoses cause intellectual disability that may worsen over the course of a person's life. In some types, vision or hearing may become impaired.
Types of Mucopolysaccharidoses
Disease Name | Comments |
|---|---|
Hurler syndrome (MPS IH) Scheie syndrome (MPS IS) Hurler-Scheie syndrome (MPS IH/S) | Start of disease: In Hurler syndrome, during the first year of life In Scheie syndrome, after 5 years of age In Hurler-Scheie syndrome, at 3–8 years of age Some symptoms: Cloudy corneas, stiff joints, heavy facial features, coarse hair, large tongue, intellectual disability, heart disease, hearing and vision impairment, inguinal and umbilical hernia, sleep apnea, fluid on the brain Treatment: Symptom relief Stem cell transplantation or bone marrow transplantation |
Hunter syndrome (MPS II) | Start of disease: Between 2–4 years of age Some symptoms: Similar to Hurler syndrome but milder and no cloudy corneas In the mild form, normal intelligence In the severe form, worsening intellectual and physical disability, death before 15 years of age Treatment: Symptom relief Stem cell transplantation or bone marrow transplantation |
Sanfilippo syndrome (MPS III)* | Start of disease: Between 2–6 years of age Some symptoms: Similar to Hurler syndrome but with severe intellectual disability Treatment: Symptom relief |
Morquio syndrome (MPS IV)† | Start of disease: Between 1–4 years of age Some symptoms: Similar to Hurler syndrome but with severe bone changes including underdeveloped bones at the top of the spine; possibly normal intelligence Treatment: Symptom relief |
Maroteaux-Lamy syndrome (MPS VI) | Start of disease: Varies but can be similar to Hurler syndrome Some symptoms: Similar to Hurler syndrome but normal intelligence Treatment: Symptom relief |
Sly syndrome (MPS VII) | Start of disease: Between 1–4 years of age Some symptoms: Similar to Hurler syndrome but more variation in severity Treatment: Symptom relief Stem cell transplantation or bone marrow transplantation |
Hyaluronidase deficiency (MPS IX) | Start of disease: At 6 months of age Some symptoms: Tumors in the soft tissues around joints, abnormally formed features, short stature, normal intelligence Treatment: Not established |
* This mucopolysaccharidosis also includes types IIIA, IIIB, IIIC, and IIID. | |
† This mucopolysaccharidosis also includes types IVA and IVB. | |
Diagnosis of Mucopolysaccharidoses
Prenatal screening tests
Based on symptoms and an examination
Bone x-rays
Sometimes imaging or other blood tests
Before birth, mucopolysaccharidoses can be diagnosed by using the prenatal screening tests amniocentesis or chorionic villus sampling.
After birth, a doctor usually bases the diagnosis on the symptoms and a physical examination. The presence of a mucopolysaccharidosis in other family members also suggests the diagnosis. Urine tests may help but are sometimes inaccurate. X-rays may show characteristic bone abnormalities.
Mucopolysaccharidoses also are diagnosed by analyzing blood cells. Genetic testing to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder is available.
Other tests are done depending on symptoms. For example, children who have heart problems may undergo the imaging test echocardiography, and children who have hearing problems may undergo audiometry.
Treatment of Mucopolysaccharidoses
Enzyme replacement
Sometimes bone marrow or stem cell transplantation
Treatment varies depending on the type.
Lifelong enzyme replacement therapy is being used to treat some mucopolysaccharidoses and may prevent the disorders from getting worse and reverse some of the complications.
Bone marrow transplantation or stem cell transplantation may help some people. However, these procedures may result in death or disability, so these treatments remain somewhat controversial.
Prognosis for Mucopolysaccharidoses
The prognosis depends on the type of mucopolysaccharidosis. A normal life span is possible. Some types, usually those that affect the heart, may cause premature death.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
National Organization for Rare Disorders (NORD): This resource provides information to parents and families about rare diseases, including a list of rare diseases, support groups, and clinical trial resources.
Genetic and Rare Diseases Information Center (GARD): This resource provides and easy to understand information about rare or genetic diseases.
